The present disclosure relates to a low voltage electromagnetic interference (EMI) filter in an electric vehicle, and more particularly, to a low voltage EMI filter in an electric vehicle reducing an EMI noise inside an electronic device, which charges a low voltage battery, and rapidly passing a noise generated during charging the low voltage battery to a vehicle sash ground.
Recently, environmentally friendly vehicles attract interests due to environmental problems, and expectations are increased in mass production and popularization of the electric vehicles among the environmentally friendly vehicles. In particular, interests are increased in a noise reducing technology in terms of the EMI according to high electric use characteristics of electronic devices of the electric vehicles. Furthermore, noise level specification for EMI is enforced to electronic device manufacturers in domestic and foreign original equipment manufacturing (OEM) fields of the electronic vehicles, and international organizations enforce criteria for reducing the EMI noise of the electronic devices. Accordingly, electronic device manufacturers meet a more and more severe environment in developing electronic devices.
The core of driving an electric vehicle lies in a battery component. In particular, there are various EMI noise components inside the electric vehicle, such as a charging noise generated in charging a battery, or a switching noise of a charger itself, and interests are increased in a technology for reducing the various EMI noises.
The EMI is a noise source of an unwanted wideband noise and means that the noise causes interference and hindrance to an electromagnetic wave.
A power source noise is largely divided into a common mode noise and a normal mode noise. First, the common mode noise indicates that noises in plus and minus ends of a power source flow in the same direction and is called a CM noise.
The normal mode noise indicates that noises in the plus and minus ends of the power source flow in different directions and is called a DM noise. Accordingly, a filter reducing the CM noise is called a CM filter, and a filter reducing the DM noise is called a DM filter.
An EMI filter includes a CM filter and a DM filter.
FIG. 1 is a view illustrating a typical EMI filter.
Referring to FIG. 1, the typical EMI filter has a structure having a DM filter 2 connected to a battery 1, and a CM filter 3 connected to the DM filter 2 having an Y capacitor 3 intervened between them.
The DM filter 2 includes a π type capacitor, and the CM filter 4 includes an inductor and a capacitor. The Y capacitor 3 draws out, to a sash ground (i.e., an earth GND), a noise component which passes through the DM filter 2.
The DM filter 2 first absorbs and reduces a noise component induced in a low voltage battery 1, which accordingly increases capacity of a capacitor and an inductance value of an inductor of the DM filter 2.
Actually, it is confirmed that a noise filtering effect in the DM filter 2 is small during measuring a noise level in an EMI test laboratory. Furthermore, since the noise induced in the low voltage battery 1 is transferred to the DM filter 2 in a mixed type of the CM noise and the DM noise, in case of analysis in terms of the DM filter 2, the CM noise passes without being filtered out and is drawn out to the sash ground (the earth) through the Y capacitor 3 without a change.
In particular, since an impedance component are various according to characteristics of each electronic device due to a connector impedance in the electronic device and a harness connected to the connector, it is difficult to determine which noise of the CM and DM noises causes a problem.
In addition, only the DM noise is filtered in a first capacitor C1, a first inductor L1, and the second capacitor C2 of the DM filter 2, and the DM and CM noises are filtered through the Y capacitor Cy1 and Cy2.
That is, since the CM noise is filtered after passing through the DM filter 2, there is no noise reduction effect in case of products having the CM noise.
FIG. 2 is a view for illustrating an effect of a noise generated when a typical EMI filter is connected to a switched-mode power supply (SMPS).
Referring to FIG. 2, the EMI filter (DM filter) 2 is installed in the battery 1 and the SMPS 5 is connected to the EMI filter (DM filter) 2.
Typically, although this kind of power supplying circuit is configured by assuming that a noise component is reduced in the EMI filter (DM filter) 2, a noise actually remains after passing the EMI filter (DM filter) 2. The noise passing through the EMI filter (DM filter) 2 may also become increased from a small noise state by the SMPS 5. Accordingly, the noise remained after passing through the EMI filter (DM filter) 2 is required to be reduced before entering the SMPS 5.
In order to reduce the noise induced in the low voltage battery, the EMI noise of the electronic device directly connected to the low voltage battery is required to be reduced and for this, the noise is first to be required to be reduced through the EMI filter.
Although a noise reducing technology through the EMI filter is extended from an industrial electronic device to an automotive electronic device, a noise reduction effect is negligible with a typical EMI filter in the automotive electronic device having high noise criteria.
In terms of characteristics of an electric vehicle, a low noise battery is weaker to a noise than a battery of an internal combustion engine according to electric driving and load characteristics.
Side effect characteristics, such as life-shortening of a battery and fuel-efficiency reduction, become high, as a noise component becomes great in the low voltage battery. Accordingly, a noise induced in the low voltage battery is necessary to be reduced. In addition, OEM companies of the domestic and foreign electric vehicle manufacturers also acutely feel this necessity.